JP3593901B2 - Lighting device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lighting device for a discharge tube.
[0002]
[Prior art]
In recent years, in a discharge tube (for example, a fluorescent lamp), a system in which a DC voltage is converted into a high-frequency AC voltage by a lighting circuit using an inverter and applied to a resonance load circuit including the discharge tube has been increasing. The resonance load circuit includes a resonance inductor and a resonance capacitor for setting a resonance frequency. Such a lighting circuit is a lighting circuit including two power semiconductor switching elements connected in a half-bridge structure between the positive and negative electrodes of a DC power supply, and applies the high-frequency AC voltage to both ends of a resonance load circuit. The waveform of the current flowing through the resonance load circuit (hereinafter referred to as resonance current) resonates with the inductor and the capacitor, and becomes a sine wave. This resonance current is controlled by changing the operating frequency of the lighting circuit. In recent years, there is a lighting device equipped with a dimming function capable of arbitrarily adjusting brightness in lighting equipment. Adjusting the brightness of the discharge tube can be achieved by changing the magnitude of the current flowing through the discharge tube. Here, assuming that the operating frequency at which the two power semiconductor elements are turned on and off alternately is fs, and the resonance frequency determined by the resonance inductor and the capacitor is fo, when fs is changed with respect to fo, the lamp current also changes. Light becomes possible. Based on this principle, the lighting circuit controls the operating frequency fs to perform dimming.
[0003]
As a conventional example for stabilizing the operating frequency of the switching element, there is a lighting circuit disclosed in Japanese Patent Application Laid-Open No. 8-45685. This circuit includes a half-bridge circuit that supplies an AC voltage to a resonance load circuit including a discharge lamp, shunts a part of the resonance current to a capacitance and a feedback transformer, and generates a half-bridge according to the secondary voltage of the feedback transformer. A control signal is applied to the high-side and low-side switching elements of the circuit to perform a self-excited operation.
[0004]
Further, as a conventional example of a lighting circuit that realizes dimming, there is a driving device as disclosed in Japanese Patent Application Laid-Open No. 8-37092. This driving device includes: 1) a timer circuit that generates a square wave having a desired frequency; 2) a high-side and low-side driving circuit that respectively drives two power semiconductor switching elements of an inverter according to a driving signal from the timer circuit; 3) a high-side dead time delay circuit and a low-side dead time delay circuit for preventing simultaneous conduction of two power semiconductor switching elements; and 4) a signal based on the low-side common potential based on the high-side common potential. And a level shift circuit for transmitting the drive signal from the timer circuit to the high side. These circuits are incorporated in one integrated circuit. In the above conventional example, it is possible to perform dimming by changing the operating frequency fs by controlling the frequency of the timer circuit.
[0005]
[Problems to be solved by the invention]
In the conventional example of JP-A-8-45685, a control signal having the same frequency as the resonance current is supplied to a half-bridge circuit by a feedback transformer. That is, the circuit is a self-excited circuit in which the operation of the half-bridge circuit continues even when no signal is externally supplied, and is particularly suitable for high-frequency operation. However, since the feedback transformer has a self-inductance, a phase difference occurs between the control signal and the resonance current, and the frequency of the control signal may deviate from an appropriate value. The operating environment of the lighting circuit built into the base of the bulb becomes high due to heat generated from the discharge tube. The characteristics of the magnetic core used in the feedback transformer change when the temperature becomes high, causing a change in inductance. Due to these fluctuations, the phase difference and the frequency may deviate from appropriate values, and a through current may flow through the half-bridge circuit to cause an increase in loss. It is desired that the lighting circuit of the bulb-type fluorescent lamp with a built-in lighting circuit be reduced in size, and the smoothing capacitor used in the converter that converts AC to DC be reduced in size by reducing the capacitance. I'm trying. The decrease in the capacity of the smoothing capacitor causes an increase in DC voltage fluctuation, and the operation of the lighting circuit becomes unstable.
[0006]
Therefore, a first problem to be solved by the present invention is to provide a lighting circuit that stably performs high-frequency operation even when a DC voltage fluctuates.
[0007]
When the conventional example of Japanese Patent Application Laid-Open No. 8-37092, which realizes dimming, is applied to a lighting device operating at a high frequency, leakage current of a level shift circuit for transmitting a drive signal from a timer circuit to a high side becomes a problem. Become. There are various types of level shift circuits, and all of them include at least one semiconductor switching element between the low side and the high side. The semiconductor switching element has a parasitic capacitance between its input and output terminals, and the parasitic capacitance is charged or discharged every time the output voltage of the lighting circuit changes. If the high-frequency lighting circuit is controlled by a conventional method, the leakage current increases, causing a problem such as an increase in loss or malfunction of noise.
[0008]
A second problem to be solved by the present invention is to provide a lighting device for a discharge tube in which high-frequency operation is also taken into consideration, in which the operating frequency of a lighting circuit is changed to enable dimming of the discharge tube.
[0009]
[Means for Solving the Problems]
The present invention has been made in consideration of the above problems, and a lighting device according to the present invention has the following configuration. That is, in the lighting device according to the present invention, the alternating current is applied to the discharge tube connected to the resonance means in accordance with the switching of the first and second semiconductor switching elements connected in series between the positive electrode and the negative electrode of the DC power supply. A current is supplied, the control terminal and the reference terminal of the first and second semiconductor switching elements are connected to each other at a common point, and a connection point where the reference terminal of the first and second semiconductor switching elements is connected to each other. Between at least one pole of the DC power supply, a resonance unit connected to a discharge tube and a first capacitor that generates a voltage synchronized with a current flowing through the resonance unit are connected in series, and the voltage of the first capacitor is changed. The voltage is applied to the control terminals of the first and second semiconductor switching elements via phase shift means for shifting the phase according to the frequency change of the resonance means.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a lighting circuit for supplying an alternating current to the discharge tube 1. The discharge tube 1 is intended for a normal fluorescent lamp having a filament or an electrodeless fluorescent lamp having no filament and generating plasma with lines of magnetic force emitted from an excitation coil. A power supply obtained by rectifying an AC power supply AC by a rectifier circuit DB constituted by a diode bridge is smoothed by a capacitor C1, and then a DC voltage is supplied to a lighting circuit of the discharge tube 1. The switching elements Q1 and Q2 connected in series are complementary. For example, the switch Q1 is an n-channel MOSFET, and although not shown, a free-wheeling diode (hereinafter referred to as QD1) is provided between a source terminal and a drain terminal. Built-in. The switch Q2 is a p-channel MOSFET, and has a freewheeling diode (hereinafter referred to as QD2) between the drain terminal and the source terminal. The drain terminal of switch Q1 is connected to the positive electrode side of capacitor C1, and the drain terminal of switch Q2 is connected to the negative electrode of capacitor C1. The source terminals of the switches Q1 and Q2 are connected at a common connection point S, and the gate terminals are connected at a connection point G. The current flowing between the drain and the source of Q1 and Q2 is controlled by the same voltage between the connection points G and S. A resonance load circuit including a capacitor Cf, a resonance inductor Lr, and resonance capacitors Cd and Cr is connected between the connection point S and the negative electrode of the capacitor C1, and a discharge tube (or fluorescent lamp) 1 is connected in parallel to Cr. Is provided. The capacitor Cd of the resonance load circuit may be omitted. Further, the resonance load circuit may be configured to be connected between the connection point S and the positive electrode of the capacitor C1. The frequency of the current flowing through these resonant load circuits is determined by each value. By the alternate switching operation of the switching elements Q1 and Q2, a bidirectional current flows through the resonance load circuit, and the discharge tube is turned on. The capacitor C2 connected between the drain and the source of the switch Q1 adjusts the voltage change time between the drain and the source of both switches. Capacitor C2 plays a similar role when connected between the drain and source of Q2.
[0011]
The gate drive circuit that controls the conduction state of the switches Q1 and Q2 includes a capacitor Cf connected on a resonance load circuit. The capacitor Cf obtains a drive voltage from a current flowing through the resonance load circuit in order to operate the gate drive circuit. One end of the capacitor Cf is set to a point F, and an inductor Lg is connected between the connection points G and F. The inductor Lg gives a phase difference between the current flowing through the resonance load circuit and the voltage between the gate and the source. Zener diodes ZD1 and ZD2 coupled in series in opposite directions are provided in parallel between the gate and the source. These function to prevent destruction of the switching elements Q1 and Q2 when an overvoltage is applied between the gate and the source. Some MOSFETs already have a built-in Zener diode for gate overvoltage protection. When such a switching element is selected, the above-mentioned Zener diode may be removed. Further, a capacitor Cgs is provided between the gate and the source to adjust a voltage change time between the gate and the source. That is, in the alternate switching operation of the switches Q1 and Q2, the switch plays a role of compensating for a dead time from when one switch is turned off and the other switch is turned on.
[0012]
In FIG. 1, at startup, when the DC voltage of the capacitor C1 increases due to a rise in the voltage of the AC power supply AC, the voltage at the connection point F, that is, the voltage at the capacitor Cf, gradually decreases with respect to the connection point S. At this time, a voltage equivalent to the voltage of the capacitor Cf is applied between the gate and the source. When the voltage between the gate and the source falls below the threshold voltage of the switching element Q2, Q2 turns on and a current flows from the connection point F to the connection point S, so that the voltage at the connection point F increases. As a result, the voltage between the gate and the source immediately exceeds the threshold voltage of Q2, so that Q2 turns off. Here, since the capacitor Cf, the capacitor Cgs, and the inductor Lg connected between the connection point F and the connection point S constitute an LC resonance circuit, a slight voltage change of the capacitor Cf causes a current flowing in the LC resonance circuit. And the voltage swing between the gate and the source increases. Due to such an oscillation phenomenon, the switches Q1 and Q2 start switching operation alternately.
[0013]
Next, the operation of the circuit of FIG. 1 will be described. The discharge tube 1 is supplied with a high-frequency current by a resonant load circuit using Q1, Q2 and Lr, Cr, Cd. Assuming that the current of the load resonance circuit is iL and the direction flowing out of the connection point S to F in FIG. 1 is defined as positive, there are four operation modes during one cycle of the current iL. Hereinafter, each operation mode will be described.
[0014]
Mode 1: When Q1 is turned on, a current iL flows from the capacitor 1 through a path of Q1, Cf, Lr, Cd, and Cr. The current iL charges the Cr and partially flows to the discharge tube 1 to flow. Also, the capacitor Cf is charged by iL, but the voltage at the connection point F with respect to the connection point S decreases. Since the voltage decrease at the connection point F decreases the gate voltage, when the gate voltage of Q1 falls below the threshold, Q1 turns off. On the other hand, the gate voltage of Q2 is higher than the threshold value of Q2, and is in an off state.
[0015]
Mode 2: When Q1 is turned off, the current iL has a positive polarity and a value, and this current continues to flow through the paths of Lr, Cd, Cr, QD2, and Cf. Note that a part of the current iL flows to the discharge tube 16 in a divided manner. The current iL charges Cf, and the voltage at the node F further decreases, so that the gate voltage also decreases. When the gate voltage falls below the threshold value of Q2, Q2 turns on. In addition, the current polarity during the mode 2 is opposite to Q2, and the current continues to flow through QD2 even if Q2 is turned on, as long as the polarity of the current does not change. Mode 2 is a period until the polarity of the current iL changes to negative.
[0016]
Mode 3: When the polarity of the current iL changes from positive to negative, Q2 is on in Mode 2, and iL flows through Q2. That is, iL flows through the path of Q2, Cr, Cd, Lr, and Cf, and Cf is charged by iL. The voltage at the node F increases due to iL, and when the gate voltage exceeds the threshold value of Q2, Q2 turns off. On the other hand, Q1 is in an off state because the gate voltage is equal to or lower than the threshold value of Q1.
[0017]
Mode 4: When Q2 is turned off, the current iL has a negative polarity and a value, and the current iL flows through Lr, Cf, QD1, the capacitors C1, Cr, and Cd due to the electromagnetic energy accumulated in Lr. Keep flowing. A part of the current iL flows to the discharge tube 16 by shunting. The current iL charges Cf, and the voltage at the node F further increases, so that the gate voltage also increases. When the gate voltage exceeds the threshold value of Q1, Q1 turns on. Further, the current polarity during the mode 4 period is opposite to that of Q1, and the current continues to flow through QD1 even if Q1 is turned on unless the current polarity changes. The period until the polarity of the current iL changes to positive is mode 2.
[0018]
As described above, the operations from mode 1 to mode 4 are performed during one cycle of the current iL, and thereafter, this operation is repeated.
[0019]
Next, the gate circuit will be described in detail. The gate circuits are distinguished by the conduction states of the Zener diodes connected to the respective switching elements. FIG. 2 shows a circuit when the zener diode is on, and has a configuration in which the zener diode and the inductor Lg are connected in series. In FIG. 2, the combined impedance Zg of the zener diode and the inductor Lg becomes inductive due to the large reactance of the inductor Lg. Here, assuming that the voltage of the capacitor Cf based on the connection point S is Vcf, the gate current flowing through the paths of Lg, ZD2, and ZD1 is ig, and the voltage between the gate and the source is Vgs, ig has a lag phase with respect to Vcf. And Vgs is also delayed.
[0020]
On the other hand, when the Zener diode is off, the gate circuit is a circuit as shown in FIG. 3, and the capacitor Cgs is connected in series with the inductor Lg. In FIG. 3, the combined impedance of Cgs and Lg is only the resistance when the capacitance or the inductiveness or the reactance of Cgs and Lg becomes the same value from the relationship between the magnitude and frequency of Cgs and Lg. Therefore, the gate current ig flowing through the impedance Zg composed of Cgs and Lg is advanced or delayed or in phase with respect to the voltage Vcf of Cf based on the connection point S. Here, when the reactance of the capacitor Cgs is larger than the reactance of Lg, that is, in the case of capacitance, the gate current ig advances with respect to the voltage Vcf of Cf with respect to the connection point S, and the gate, which is the voltage across Cgs, The voltage Vgs between the sources also advances.
[0021]
Here, the operation of the gate circuit when the DC voltage applied to the lighting circuit changes as shown in FIG. 4 will be described. For example, in the ordinary fluorescent lamp in which the discharge tube 1 of FIG. 1 includes a filament, when the DC voltage increases, the equivalent resistance RL of the fluorescent lamp decreases, and the combined capacitance on the resonant load circuit of FIG. The resonance frequency fo determined by the capacitance and the resonance inductor Lr decreases as shown in FIG. FIG. 5 shows the frequency characteristics of the gate circuit of FIG. FIG. 5 shows the phase difference φg of the gate voltage Vgs with respect to the resonance current iL and the voltage Vs at the connection point S, that is, the phase difference φ of the resonance current iL with respect to the output voltage of the inverter, and the operating frequency fs when the resonance frequency fo changes. FIG. 6 shows waveforms of the gate voltage Vgs, the resonance current iL, and the voltage Vs at the connection point S. From FIG. 5, as the resonance frequency fo increases, the phase difference φg decreases from φg1 to φg2. This is because if the impedance Zg of the series circuit composed of Cgs and Lg in FIG. 3 is capacitive, the impedance of the gate approaches inductive due to the increase in the resonance frequency fo. As a result, the gate current ig flowing through the series circuit is delayed, the voltage Vgs between the gate and the source, which is the voltage across Cgs, is delayed from the waveform shown by the broken line in FIG. 6 to the waveform shown by the solid line, and the phase difference φg is reduced. Also, as shown in FIG. 6, the voltage Vs at the connection point S is delayed from the waveform shown by the broken line to the waveform shown by the solid line, and the phase difference φ is reduced from φ1 to φ2 in FIG.
[0022]
On the other hand, in the case of the self-excited lighting circuit as shown in FIG. 1, the operating frequency fs increases as the resonance frequency of the load increases as shown in FIG. However, as described above, since the phase difference φ decreases from φ1 to φ2, from the relationship between the phase difference φ and the operating frequency fs shown in FIG. 7, fs slightly increases from fs1 to fs2, and the operating frequency fs The increase is suppressed. That is, the phase difference φg is automatically adjusted so as to reduce the change Δfs in the operating frequency with respect to the change Δfo in the resonance frequency. The capacitance of the capacitor C1 is set so that the change in the DC voltage is as small as possible. However, since the capacitor C1 has a relatively large shape among components used in the lighting circuit, it is desirable to reduce the capacitance and reduce the size. It is. When the capacitance of the capacitor C1 is reduced as described above, the change of the DC voltage increases, but the self-excited operation can be stably continued in response to the DC voltage and the load fluctuation by the above-described operation.
[0023]
Next, a method for adjusting the brightness of the discharge tube will be described. In recent years, there is a lighting device equipped with a dimming function capable of arbitrarily adjusting brightness in lighting equipment. Adjusting the brightness of the discharge tube can be achieved by changing the magnitude of the current flowing through the discharge tube. In the resonance load circuit, the relationship between the operating frequency fs of the lighting circuit and the resonance current iL is as shown in FIG. 8, and as the operating frequency fs is increased with respect to the resonance frequency fo determined by the resonance inductor and the capacitor, the current of the discharge tube increases. Decrease. Based on this principle, the lighting circuit controls the operating frequency fs to perform dimming. The dimming of the incandescent lamp is performed by controlling the flow angle of the AC power supply AC by a dimmer using a triac and adjusting the power supplied to the light bulb. According to the present invention, in a lighting circuit using an inverter, for example, when a converter that outputs a DC voltage in accordance with AC whose flow angle is controlled by a dimmer is used, a discharge tube corresponding to a change in the DC voltage is used. Brightness can be adjusted. When the DC voltage changes, the resonance frequency of the load also changes as shown in FIG. In the above description, the phase difference φg of the gate voltage was adjusted so as to reduce the change in the operating frequency with respect to the change in the resonance frequency, and the self-excited operation was continued. In the lighting circuit described here for the purpose of dimming, the discharge tube is dimmed by increasing the change in the operating frequency fs with respect to the change in the resonance frequency fo.
[0024]
FIG. 9 shows a configuration of a gate circuit that realizes dimming. FIG. 9 shows a configuration of a gate circuit in which a capacitor Cg is provided in parallel with the inductor Lg of FIG. 3, and shows a case where the Zener diode is off. In FIGS. 3 and 9, the same components have been described above with reference to FIG. 3, and description thereof will be omitted. In FIG. 9, the combined reactance of the capacitors Cgs, Cg and the inductor Lg is only capacitive or inductive, or only the resistance due to the relationship between the magnitudes and frequencies of Cgs, Cg and Lg. Therefore, the current ig flowing through the gate circuit is advanced or delayed or in phase with respect to the voltage Vcf of Cf based on the connection point S. Here, the reactance Xc of the capacitor Cg decreases and the reactance XL of the inductor Lg increases as the resonance frequency increases. When the reactance Xc becomes smaller than XL, the combined impedance of the gate circuit becomes capacitive, and the current iL flowing in the gate circuit advances with respect to the voltage Vcf of Cf with respect to the connection point S. As a result, the voltage Vgs between the gate and the source, which is the voltage across Cgs, also has an advanced phase, and the phase difference φg with respect to the resonance current iL increases. In this way, by connecting the capacitor Cg in parallel with the inductor Lg, when the resonance frequency increases, the phase difference φg of the gate voltage can be increased as shown in FIG. 10 to increase the phase difference φ. That is, since the increase in the phase difference φ increases the operating frequency fs, the change Δfs in the operating frequency with respect to the change Δfo in the resonance frequency can be increased. Further, the gate drive circuit of FIG. 9 of the present invention uses the voltage of the capacitor Cf connected to the resonance load circuit, so that when the resonance frequency increases, the reactance of the capacitor Cf decreases and the voltage Vcf of the Cf also increases. Decrease. Vcf and the gate voltage Vgs are in a proportional relationship, and Vgs decreases as Vcf decreases. FIG. 11 shows operation waveforms when the amplitude of the gate voltage increases and decreases when the resonance frequency fo changes. In FIG. 11, the operation waveform when the resonance frequency fo is low is indicated by a broken line, and the amplitude of the gate voltage Vgs increases. When Vgs is large, the phase difference φ between the voltage Vs at the connection point S and the resonance current iL becomes small. On the other hand, when the resonance frequency fo increases, the operation waveform becomes as shown by the solid line, and the amplitude of the gate voltage Vgs decreases. As Vgs decreases, the phase difference φ increases. The present invention that performs gate drive by feeding back the voltage of the capacitor Cf on the resonance load circuit differs from the gate drive using a conventional feedback transformer in that the gate voltage is reduced when the resonance frequency fo increases to increase the phase difference φ. And works to increase the operating frequency fs. Summarizing the above, the gate circuit as shown in FIG. 9 adjusts the phase difference φg of the gate voltage, and further adjusts the amplitude of the gate voltage Vgs by using the capacitor Cf, thereby changing the resonance frequency change Δfo. On the other hand, dimming is performed by increasing the change Δfs in the operating frequency.
[0025]
The starting in the above-described embodiment has a circuit configuration in which the capacitor Cf connected on the resonance load circuit is charged according to the DC voltage and starts operation. On the other hand, FIG. 12 shows a lighting circuit using a starting capacitor other than the capacitor Cf. FIG. 12 shows a configuration in which the starting capacitor Cs is connected to FIG. 1. In FIG. 1 and FIG. 12, the same components have been described above with reference to FIG. 1, and the description thereof will be omitted. The starting capacitor Cs is connected between the connection point G and the connection point F in series with the inductor Lg. A resistor R1 is connected between the positive electrode of the capacitor C1 and the connection point G, and a resistor R2 is connected between the connection point S and the negative electrode of the capacitor C1. Further, a resistor Rd is connected in parallel to the capacitor Cf. At the time of starting, the starting capacitor Cs is charged via the resistors R1, R2, and Rd as the DC voltage increases, and a voltage substantially equal to the voltage of the starting capacitor Cs is applied between the gate and the source. When the voltage between the gate and the source exceeds the threshold voltage of the switching element Q1, Q1 turns on, a current flows from the connection point S to the connection point F, and the voltage of the connection point F, that is, the voltage of the capacitor Cf decreases. Here, since the capacitor Cf, the starting capacitor Cs, the capacitor Cgs, and the inductor Lg connected between the connection point F and the connection point S constitute an LC resonance circuit, a slight voltage change of the capacitors Cs and Cf causes , The current flowing through the LC resonance circuit increases, and the voltage amplitude between the gate and the source increases. Due to such an oscillation phenomenon, the switches Q1 and Q2 start switching operation alternately. After the start of the operation, the resistor Rd connected in parallel with the capacitor Cf has an effect of reducing the DC component of the voltage generated in the capacitor Cf, and does not adversely affect the operation. That is, Rd equalizes the positive and negative voltage amplitudes generated in Cf, makes the conduction periods of the upper and lower switching elements equal, and stably maintains the operation of the lighting circuit. The embodiment using the starting capacitor can be modified in addition to the above-described configuration, and a configuration in which Cs is connected in series with a resistor between the connection points G and S in FIG. 12 may be used.
[0026]
FIG. 13 shows a lighting circuit in which a starting inductor Ls is connected between a connection point S and a connection point F in series with a capacitor Cf. In the above description, a slight voltage change of the capacitor Cf or the starting capacitor Cs is used as a starting pulse to increase the voltage amplitude between the gate and the source. However, by using the starting inductor Ls as shown in FIG. A large induced voltage can be obtained with a small current, and reliable starting is possible. After the start of the operation, the self-excited operation is not adversely affected by selecting the reactance of the capacitor Cf to be much larger than the reactance of the starting inductor Ls.
[0027]
【The invention's effect】
According to the present invention, the high frequency operation of the lighting device is stabilized.
[Brief description of the drawings]
FIG. 1 shows a first embodiment of a lighting circuit according to the present invention.
FIG. 2 is a gate circuit when the zener diode of FIG. 1 is in a conductive state;
FIG. 3 is a gate circuit when the Zener diode of FIG. 1 is not in a conductive state;
4 is a graph showing a relationship between a DC voltage change in FIG. 1 and an equivalent resistance and a resonance frequency of a discharge tube.
FIG. 5 is a graph showing a relationship between a phase difference between a resonance current and a gate voltage with respect to a resonance frequency of the gate circuit of FIG.
FIG. 6 is an operation explanatory diagram of the embodiment of FIG. 1;
FIG. 7 is a graph showing the relationship between the inverter output voltage and the phase difference of the resonance current with respect to the operating frequency of the embodiment of FIG.
FIG. 8 is a graph showing a relationship between an operating frequency of a lighting circuit and a resonance current in a resonance load circuit.
FIG. 9 is a gate circuit for dimming according to the present invention.
10 is a graph showing the relationship between the resonance current versus the gate voltage phase difference and the inverter output voltage versus the resonance current phase difference and operating frequency with respect to the resonance frequency of the gate circuit of FIG.
FIG. 11 is an operation explanatory diagram of the gate circuit in FIG. 9;
FIG. 12 shows a second embodiment of the lighting circuit according to the present invention.
FIG. 13 shows a third embodiment of the lighting circuit according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Discharge tube, AC ... AC power supply, DB ... Rectifier circuit, Q1, Q2 ... Power MOSFET, ZD1, ZD2 ... Zener diode, Zg ... Impedance, C1, C2, Cd, Cr, Cf, Cgs, Cg, Cs ... Capacitor , Lg, Lr, Ls... Inductor, R1, R2, Rd.

Claims (10)

A lighting device for supplying an alternating current to a discharge tube connected to a resonance unit in accordance with switching of first and second semiconductor switching elements connected in series complementarily between a positive electrode and a negative electrode of a DC power supply,
The control terminal and the reference terminal of the first and second semiconductor switching elements are connected to each other at a common point,
A resonance unit connected to the discharge tube between a connection point where the reference terminals of the first and second semiconductor switching elements are commonly connected and at least one pole of the DC power supply; And a first capacitor that generates a voltage that is connected in series,
The voltage of the first capacitor is applied to control terminals of the first and second semiconductor switching elements via phase shift means for shifting a phase according to a frequency change of the resonance means. Lighting device. 2. The lighting device according to claim 1, wherein the phase shift unit is a first inductor, and includes a gate drive circuit including the first inductor and the first capacitor. 3. The device according to claim 2, further comprising a second capacitor for limiting a voltage change at a control terminal between the control terminal and the reference terminal of the first and second semiconductor switching elements. A lighting device comprising a gate drive circuit including one inductor. 4. The device according to claim 3, further comprising a clamp between the control terminal and the reference terminal of the first and second semiconductor switching elements to limit a voltage of the control terminal to an allowable value or less. A lighting device comprising: a gate drive circuit including a capacitor and the first inductor. 5. The lighting device according to claim 4, further comprising a third capacitor between the common connection point of the reference terminals of the first and second semiconductor switching elements and at least one pole of the DC power supply. 6. The lighting device according to claim 5, further comprising a starting unit configured to apply a starting voltage to the first capacitor. 3. The lighting device according to claim 2, further comprising a fourth capacitor in parallel with the first inductor, and a gate drive circuit including the first and fourth capacitors and the first inductor. . 3. The device according to claim 2, further comprising a starting capacitor connected between a positive electrode and a negative electrode of the DC power supply via a resistor, and controlling a voltage of the starting capacitor to control terminals and a reference terminal of the first and second semiconductor switching elements. A lighting device characterized in that a voltage is applied between the lighting devices. 3. The device according to claim 2, further comprising a second starting inductor in series with the first capacitor, and a gate drive circuit including the first and second inductors and the first capacitor. Lighting device. An illumination apparatus comprising: the lighting device according to claim 1; and an electrodeless fluorescent lamp as the discharge tube.

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